This application relates to magnetic disc drives and more particularly to the incorporation of drag reduction features within the disc drive to reduce vibrations on the actuator assembly and read/write heads caused by air turbulence and drag loads on the actuator assembly.
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are coated with a magnetizable medium and are mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (xe2x80x9cheadsxe2x80x9d) mounted to a radial actuator for movement of the heads relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The read/write transducer, e.g. a magnetoresistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment. Critical to both of these operations is the accurate locating of the head over the center of the desired track.
The heads are mounted via flexures or suspensions at the ends of a plurality of actuator arms that project radially outward from the actuator body. The actuator body pivots about a shaft mounted to the disc drive housing at a position closely adjacent the outer extreme of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs, so that the heads move in a plane parallel with the surfaces of the discs. Alternatively, linear actuators may be used in place of rotary actuators to move the heads in a linear direction along a radial line of the discs. Regardless of whether a rotary or a linear actuator mechanism is utilized, the heads are typically mounted on a slider (e.g., a ceramic block) having a specially etched air bearing surface that forms an air cushion or xe2x80x9cbearingxe2x80x9d as the disc rotates beneath the slider. The hydrodynamic lifting force provided by the air bearing surface counters an opposing preload force supplied by the suspension and causes the slider to lift off and xe2x80x9cflyxe2x80x9d a very small distance above the surface of the disc. Although the fly height of the slider is only a fraction of a micron, this thin film of air between the slider and the disc prevents damage to the fragile magnetic coating on the surface of the disc.
The current generation of disc drives rotates faster and writes data on data tracks that are more closely spaced together than on prior disc drives. Thus, it has become more difficult on these current disc drives to maintain the read/write head centered over a particular disc track as the disc is spinning. Any error in the position of the head relative to the desired track can lead to improper read or write operations and ultimately to data loss.
The ability to maintain the proper head position is made even more difficult by the aerodynamic conditions within the disc drive. As noted above, air within the disc drive is pulled along with the spinning discs to form the cushion or xe2x80x9cbearingxe2x80x9d that allows the head to fly at a very low altitude over the disc surface. This airflow is often quite turbulent, particularly where the discs rotate at a relatively high rate of speed, and the impact of the turbulent airflow on the actuator arm and suspension causes the suspension (and thus the head) to vibrate in a random manner.
In an effort to reduce the turbulent nature of the airflow within a disc drive, some drive manufacturers have added one or more air dams to the disc drive as shown in U.S. Pat. No. 6,097,568, entitled xe2x80x9cAir Dams Positioned Between Spinning Disks for Reducing the Vibration in a Data Storage Device.xe2x80x9d Such air dams include an arm positioned in the airspace between two adjacent discs to provide an obstruction to the airflow, thereby reducing the energy of the airflow so that the actuator arm/suspension experiences a less turbulent flow. However, it has been found that the presence of such air dams within the enclosed disc drive can often create turbulence as the airflow passes over the air dam. Specifically, as most air dams have a rectangular cross section, it is known that flow separation can occur as the airflow passes over the fingers of the air dam, thereby creating a low pressure area and turbulent eddies immediately downstream of the air dam. These turbulent eddies propagate throughout the drive and ultimately impact the actuator arm/suspension to cause undesired vibrations in the read/write head. Furthermore, it has been observed that the presence of conventional air dams immediately upstream of the actuator assembly can create sufficient additional turbulence that the power requirement of the disc drive (i.e., the power requirement of the spindle motor) is actually increased due to increased xe2x80x9cskin friction dragxe2x80x9d between the airflow and the surfaces of the disc.
As an alternative to air dams, manufacturers may choose to add structures such as shrouds to closely surround the rotating discs and thereby direct or channel the air within the disc drive in a controlled manner. One such shroud is shown in U.S. Pat. No. 5,696,649, entitled xe2x80x9cElastic Insert Shroud to Provide Maximum Effective Shrouding Shock Mitigation and Filtering in High Speed Disk Drives.xe2x80x9d
A further alternative is to streamline the leading edge of the actuator arm/suspension to reduce the impact of the turbulent flow on the actuator arm. Such a design is shown in U.S. Pat. No. 5,999,372, entitled xe2x80x9cActuator Arm with Streamlined Leading Edge to Reduce Air Turbulence,xe2x80x9d which patent is assigned to the assignee of the present application. This patent describes streamlining the leading edges of the actuator arm/suspension as a way to reduce turbulence within the disc drive, thereby reducing the xe2x80x9cskin friction dragxe2x80x9d on the discs and the power requirement of the spindle motor. That is, this patent describes the creation of a more laminar flow within the disc drive. However, laminar flow is more likely than a turbulent flow to become separated from an object (such as an actuator arm) as the airflow passes over and around the object. Such flow separation leads to relatively high levels of xe2x80x9cpressure dragxe2x80x9d which is caused by areas of low pressure behind the object, as noted above.
Thus, prior art attempts to reduce airflow induced vibrations on the actuator arm/suspension have concentrated on adding additional structure to reduce the amount of turbulent airflow within the disc drive. However, while the use of air dams, shrouds and tapered actuator arms/suspensions may create a more laminar flow between the discs, relatively large levels of pressure drag may still be experienced by the actuator arms/suspensions as the airflow separates from these structures.
Accordingly, there is a need for reducing the level of airflow induced vibrations experienced by the actuator arm/suspension of a disc drive. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
The present invention relates to a disc drive having surface features that reduce the drag forces experienced by the actuator assembly during operation of the disc drive, thereby reducing read/write errors due to drag-induced vibrations on the heads of the disc drive.
In accordance with one embodiment of the present invention, a disc drive includes a disc mounted for rotation on a spindle motor, and an actuator assembly for moving a head above the surface of the disc. The actuator assembly includes an actuator arm and a suspension, wherein the suspension includes a load beam connected at one end to a distal end of the actuator arm and at an opposite end to the head. The actuator assembly includes a plurality of surface features formed on a surface of at least one of the actuator arm and the load beam to reduce an aerodynamic drag force experienced by the actuator assembly.
In one embodiment of the invention, the surface features comprise a plurality of dimples formed in a surface of at least one of the actuator arm and the load beam. Alternatively, the surface features may comprise a plurality of V-shaped denticles formed on a surface of at least one of the actuator arm and the load beam. In another preferred embodiment, the surface features are formed on top and bottom surfaces of the actuator arm, while in other embodiments the surface features are formed on top and bottom surfaces of the load beam. Additionally, in one embodiment of the invention, the surface features are formed on both the actuator arm and the load beam, and the features formed on the load beam are smaller than the features formed on the actuator arm.
In a further embodiment of the invention, the disc drive may include an air dam having a finger extending over the surface of the disc. The finger has a plurality of surface features formed on top and bottom surfaces of the finger to reduce flow separation of an airflow passing over the finger. As with the actuator assembly, the surface features on the finger may comprise a plurality of dimples or a plurality of raised V-shaped features similar to shark skin denticles.
The present invention can also be implemented as an actuator assembly for a disc drive, where the actuator assembly comprises an actuator arm and a suspension which in turn comprises a load beam for supporting a head above a surface of a disc. The actuator assembly includes a plurality of surface features formed on a surface of at least one of the actuator arm aid the load beam to reduce aerodynamic drag forces experienced by the actuator assembly. In one preferred embodiment, the load beam includes a top surface, a bottom surface, and stiffening rails extending upward from the top surface along opposite sides of the load beam, and the surface features are formed on top and bottom surfaces of the actuator arm and on the bottom surface of the load beam.
The present invention can further be implemented as a disc drive assembly having a disc mounted for rotation on a spindle motor, and an actuator assembly extending within a flow of air created by the rotating disc. The actuator assembly includes an actuator arm and a suspension for positioning a head above the disc surface. The disc drive assembly further includes means for reducing aerodynamic drag on the actuator assembly to reduce drag-induced vibrations on the head. In one preferred embodiment, the means for reducing aerodynamic drag on the actuator assembly includes a plurality of surface features formed on at least one of the actuator arm and the suspension. In a further preferred embodiment, the means for reducing aerodynamic drag on the actuator assembly includes an air dam having a plurality of surface features to reduce flow separation of an airflow passing over the air dam.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.